Electric circuit breaker



July 12, 1932. E. B. WEDMORE ET AL ELECTRIC CIRCUIT BREAKER Filed May22, 1929 2 Sheets-Sheet 1 mum I w/ud July 12, 1932. E. B. WEDMORE ET- ALELECTRIC C IRCUIT BREAKER Filed May 22, 1929 2 Sheets-Sheet 2 5 Jaw 2Patented July 12, 1932 UNITED STATES PATENT OFFICE EDMUND BASIL WEDMOREAND WILLIS BEVAN WHITNEY, OF LONDON, ENGLAND, ASSIGNORS TO THE BRITISHELECTRICAL AND ALLIED INDUSTRIES RESEARCH ASSOCIATION, OF LONDON,ENGLAND, A BRITISH ASSOCIATION ELECTRIC CIRCUIT BREAKER 'Applicationfiled May 22, 1929, Serial No. 365,081, and in Great Britain June 8,1928.

This invention consists in improvements in or relating tocircuit-breakers for use in circuits carrying. electric power, and isparticularly, although not exclusively, applicable to circuits whereinthe electrical pressure is relatively high, say of the order of 10,000or more line volts, more especially to circuits of the higher voltages.

It is now generally appreciated that it is important, in the case, forexample, of power circuits, so to arrange conditions that in thebreaking of the circuit the arc will not reform. after the current hasreached zero value. In highly inductive circuits, however, the fullelectrical pressure of the circuit may come upon the contacts of thecircuit-breaker almost immediately after the current has reached thezero value, thus causing the arc to reform. In the neighbourhood of thearcroot on the contacts when the breaker is operating, the temperatureis likely to be high, thus facilitating ionization (corona formation)and breakdown in this part at the time of zero current, while at thesame time the tendency to breakdown of the different parts of the gapbetween the contacts varies with the gaseous content, temperature,pressure, and previous history of the arc.

It is generally recognized that it is advantageous to reduce'the amountof energy produced in the breaker itself during the operation ofbreaking cireuit; and with this in view, the general object of thepresent invention is so to improve circuit-breakers for use in powercircuits, that they will be more reliable in operation than breakersheretofore constructed and will operate with less production of energywithin them in making and breaking of the circuit.

It is known that the density of an electrostatic field on the surface ofa charged body depends, amongst-other factors, on the shape of thatsurface, the density being greatest at the most abrupt or pointedportions of that surface. The use of corona shields around the fixedcontact for preventing corona under normal running conditions is known,see, for example, prior British Patent No. 19583/11. In such designs,when the moving contact leaves the fixed contact, no

attempt has been made to prevent formation of corona on the movingcontact. It will be understood that corona on the moving contact willcease after the circuit has been broken and the gap filled with oil sothat its existence is only momentary and this has been consideredsatisfactory in the past.

We find, however, that it is of great advantage to suppress theformation of all corona in the arc gap while the circuit is beingbroken, and according to our invention, corona shields are provided foreach contact so designed as to suppress or prevent the formation ofcorona on the contacts at both ends of the gap. One result obtaining bymeans of our invention is the approximate adjustment of the fieldgradient to'the strength of the different parts of the gap so as towithstand maximum voltage across a given ap. The guard or shield deviceis applica le on occasions to both the main and the arcing contacts. Theinvention is applicable to circuitbreaking apparatus having separablecontacts or separated contacts includin such of the latter as areconnected by a fus1ble link.

In the case of a multiple-break circuitbreaking apparatus having aplurality of pairs of separable or separated contacts, the contacts ofeach pair are provided with corona shields.

For a given voltage, we are thus able to use a much shorter gapespecially on very high voltages with a consequent reduction in areenergy and burning of contacts.

Preferably, one or each shield is movable relatively to its own contactin the direction of separation, and in one preferred form of theinvention, each such moving shield iscombined with a spring orequivalent means which serves to urge the shield towards the companionshield. Thus, as the contacts are closed, the movable shield jor shieldsmay be I pressed back to allow such closure and, when the contactsseparate, the shield or shields are moved forward again to a position infront of or beyond the ends of their respective contacts. It is notessential that after said contacts have separated the shield or, shieldsshould move forward beyond the contact or contacts which they guard, aswe fin breaker so that said moving contact or contacts move through ortowards or level with an aperture in said shield or shields, beingelectrically connected with said shield or shields by flexible or othersuitable connections.

In a modified form of apparatus according to this invention, one shieldmay be of smaller diameter than the other so that it may enter insidethe companion shield when the breaker contacts are closed, thus avoidingthe necessity for having one or both shields relatively movable inrelation to their respective contacts. Where the shield or shields arewithin or .near the arcing zone, it is desirable to insulate theirexposed surfaceswith solid insulating material so that the arc cannotcome into contact with the conducting material of which they are formed.

In order that the invention maybe more clearly understood, oneconstruction will now be described with the aid of the accompanyingdrawings, in which Figure -1 illustrates more or less diagrammatically asection through a pair of contacts of a circuit-breaker, the sectionbeing taken in a plane containing the axis of the arc path,

Figure 2 is a section on the line 2-2 of Figure 1 and Figure 3 is a viewsimilar to Figure 1 of a modified construction.

Like reference numerals indicate like parts in both figures of thedrawings.

The upper or female contact 10 is intended to be fixed, and the lower ormale contact 11 is movable, and for this purpose is carried, in theexample illustrated, by a cross-bar 12, at the other end of which thereis another similar movable contact to be associated with a fixed contactfor a double-break circuitbreaker. Alternatively, the contacts shown maybe considered as those of a single-break circuit-breaker, and thecross-bar 11 can be considered as any moving carrier by which themovable contact is supported.

Surrounding the two contacts 10 and 11 are shields 13 and 14respectively, each covered with insulating material indicated at 15. Theshields are respectively in the form of rings supported by arms 16 and17. The arms 16 of the shield 13 are bolted to a collar 18 that is fixedinvelect-rical connection with the contact 10. The arms 17 are bolted toa collar 19 which is a sliding fit on the movable contact 11 and ismaintained in 00d electrical connection with that contact y means of aconducting strip 20.

It will be seen that the ring 13 is retained at a position beyond theextremity of its associated contact 10 and, when the contacts are open,as shown in Figure 1, the shield 14 is retained in a similar mannerbeyond the end of its contact 11 by means of a coiled compression spring21. When the contacts are to be closed, however, the insulation coveringthe shield 14 will contact with that covering the shield 13 so that theshield 14 is pressed back against the spring 21 to permit the contact 11to enter the contact 10.

The shield 13, in one modification, may be similarly slidably mounted onor in association with the fixed contact 10 so that both shields may bepressed backwardly to some extent during the close of the contacts. Inthe modified construction shown in Figure 3, the diameter of the shield14 is smaller than the internal diameter of the shield 13 so as to allowthe shield 14 to enter within the latter, and the shield 14 is carriedin fixed ple wood, which is soaked with oil or other 'moinsulatingliquid.

Figure 1, which represents the shields and contacts in the course ofcontact separation, is an example of one type of shielding devicesuitable for guarding contacts on a switch handling about 10,000 R. M.S. volts per break or for mounting on a triple pole, 33,000 volt switchhaving a total of six breaks, the mean diameter of the upper guard ringin Figure 1 would in this case be about 5" but mention of this dimensiondoes not preclude use of other sizes or dimensions.

We claim 1. Circuit-breaking apparatus comprising in combinationrelatively movable contacts affording at least one gap between which anarc may form, a guard of conducting material for and electricallyconnected to each arcing contact for modifying the distribution ofpotential in the gap between the contacts, one at least of the guardsbeing movable relatively to its own contact in the direction of relativemovement of the contacts.

2. Circuit-breaking apparatus comprising in combination relativelymovable contacts afiording at least one gap between which an arc mayform, a guard of conducting material for and electrically connected toeach arcing contact for modifying the distribu tion of potential in thegap between the contacts, one at least of the guards being movablerelatively to its own contact in the direction of relative movementbetween the contacts, and means associated with said movable guardserving to urge the latter towards its companion guard and, when thecontacts have been separated, to move the guard beyond the extremity ofits own contact considered in the direction towards the adjacentcontact.

3. Circuit-braking apparatus comprising in combination relativelymovable contacts afiording at least one gap between which an arc mayform, a guard of conducting material for and electrically connected toeach arcing contact for modifying the distribution of potential in thegap between the contacts, one at least of said guards being movablerelatively to its own contact in'the direction of relative movement ofthe contacts, said movable guard being carried on and movable with itsassociated contact.

4. Circuit-breaking apparatus comprising in combination relativelymovable contacts affording at least one gap between which an arc mayform, a guard of conducting material for and electrically connected toeach. arcing contact for modifying the distribution of potential in thegap between the contacts, one at least of said guards being movablycarried on its own contact so as to be movable therewith and relativelymovable thereto in the direction of movement of the contacts, and meansassociated with said movable guard serving to .urge the latter towardsits companion guard and, when the contacts contact being itself movablerelatively to its own contact in the direction of relative movementbetween the said two contacts.

6. Circuit breaking apparatus for the rupture of electric power circuitson load comprising in combination a fixed contact and a movable contactbetween which an arc may form and at least one guard of conductingmaterial for and electrically connected to each arcing contact formodifying the distribution of potential in said gap, the guard for thefixed contact being mounted on a fixed part and the guard for themovable contact being movable with said contact, one at least ofsaidguards being movable relatively to its own contact in the direction ofrelative movement between the contacts, means associated with saidmovable guard servingto urge the latter towards 1ts companion guard anda separating member of insulating material on at least one of saidguards serving to prevent electrlcal contact between said guards."

7. Circuit breaking apparatus for the rupture of electric power circuitson load comprising in combination a fixed contact and a movable contactbetween which an arc may form and at least one guard of conductmmaterial for, electrically connected to an carried by each arcingcontact for modifying the distribution of potential in said gap, one atleast of said guards being movable relatively to its own contact in thedirection of relative movement between the contacts, means associatedwith said relatively movable guard serving to urge the latter towards1ts companion guards and a separating member of insulating material onat least one of sand guards serving to prevent electrical contactbetween said guards, the parts being arranged, so that when the contactsare closed the relatively movable guard is situated behind the tip ofits contact but in front of 1t when they are separated.

In testimony whereof we have signed our names to this specification.

EDMUND BASIL WEDMORE. WILLIS BEVAN ,WHITNEY.

